1. Field of the invention
The present invention relates to a turbine guide blade or vane of the type which is swept internally by cooling air, the outer wall of the blade bounding an interior space and having an aerodynamic outer profile defining the leading edge of the said blade, its extrados face, its trailing edge, and its intrados face.
2. Summary of the prior art
Industrial and commercial competition causes aircraft engine manufacturers to seek constantly to improve the performance of turboshaft engines. Such improvement may be obtained by raising the temperature of the gases at the inlet of the turbine. The part most affected by these high temperature levels is the first stage of the fixed guide blades, and several solutions have already been proposed for the cooling of these guide blades.
Published French Patent Application No. 2 290 569 proposes placing an insert inside the internal space of the blade, the outer wall of the blade having on its inner face axial projections communicating in the vicinity of the leading edge with the inner cavity of the insert. In this construction, the leading edge is cooled by the impact of the air issuing from the inner cavity of the insert. However, difficulties may be encountered in equalizing the volumes of cooling air emitted between the root of the blade and the head of the blade, and equalizing the temperatures in the blade section.
U.S. Pat. No. 4,153,386 discloses a guide blade in which the internal space of the blade is divided into two ducts and has inserts provided with holes for the escape of air towards the outer wall. In this construction, the air is evacuated along the inlet ducts and flows axially near the outer wall of the blade to cool said wall.
U.S. Pat. Nos. 3,574,481 and 2,879,028 describe blades in which an internal duct is supplied with air, and the air escapes along this duct through openings and flows axially in the vicinity of the outer wall of the blade.
Published GB Patent Application No. 2 184 492 discloses a movable blade having a plurality of radial passages communicating with small diameter ducts connected to the outside of the blade by a plurality of holes. Here also, the air escapes progressively from the root of the blade.
In all the blades described above, the volume of cooling air decreases progressively from one end of the blade.
Published French Patent Application No. 2 460 387 discloses a hollow blade in which cooling ducts are provided in the outer wall of the blade, the blade wall being provided with extra thickness in the vicinity of the hotter areas. This document does not mention the possibility of a cooling air curtain along the outer surfaces of the blade, and the blade cannot therefore be a guide blade mounted at the head of a turbine.